The present invention relates to conveyor systems and more particularly to zone control systems for conveyor systems.
Conveyor systems move desired payloads from one place to another in an orderly fashion. Rollers or belts are used to move the payloads. An example of a payload may be a cardboard box, a shipping container, a wooden pallet, or an automotive steel component. Within a conveyor system, there are often points, often called stations, along its length with varied equipment used to do work on the payload as it moves to its end destination. At each station an action or function is performed on the payload. Depending on the function to be performed, the conveyor may stop, a payload may be removed, or the conveyor may continue to move the payload. In addition to these stations, there are often merges, diverges, and intersections with other conveyors systems that moves the payload to and from those conveyor systems. A large number of inputs and outputs are used to do the handshaking between systems.
Although some conveyor systems simply move the payload from point A to point B, there is often a need to control the movement of payloads along its length. There are entrance and exit points of the conveyor that requires input and control signaling to stop and start the flow of the conveyor. These controls are required for interfacing with the various stations along its path. A frequently used type of control is called Zero Pressure Accumulation or (ZPA) which is a common industry term used to describe the separation of payloads as they are moved down the conveyor. ZPA controls the movement of the payloads, placing appropriate space between the payloads. ZPA avoids having a stack up of payloads queuing at the end of a conveyor where the pressure builds on the end payload, possibly causing damage.
To achieve the control necessary for the above action on a conveyor, the conveyor is divided ‘n’ number of fixed length sections or zones. A zone is of fixed physical length. The mechanism to control a zone varies widely. It can be a set of rollers interconnected that moves the payload through the zone. It could be one belt driven on top of a set of rollers moving the payload. Or a set of 2 or 3 chains linked together to move the payload. A zone can be driven using electric motors, hydraulics, pneumatics, or other types of methods. The common feature of all these drive mechanisms is that a command is given to activate or deactivate the zone.
Each zone is responsible for moving the payload into its zone, holding the payload, and discharging it to the next zone. An electronic device called a zone controller is usually used to control the action that occurs within the zone. Since a conveyor is divided into ‘n’ numbers of zones, there will also be ‘n’ number of zone controllers. Excluding the entry and exit zone, each zone interfaces to its adjacent neighbors to help determine its control. There are various methods of control and communications used to control the movement of the payload down the conveyor from entry to exit zones.
In one example, hardware inputs and outputs are used for signaling between adjacent controllers. This greatly restricts the data that can be communicated. It also requires individual wiring between controllers that is expensive and time consuming to assemble.
Another example uses serial communication between adjacent controllers. This gives the ability to communicate more detailed data between adjacent controllers, but the data the two controllers communicate is not shared outside of themselves.
In another example, serial communication is used between controllers as above, and the data is daisy-chained (or passed) through to the next adjacent controller, and the next adjacent controller, etc. This methodology provides the means for a zone controller to send and receive data with other zone controllers in the system. But as the number of conveyor zones increase, the number of data messages to pass through a zone controller increases dramatically, and consumes zone controller resources. The data messages are kept very short and the amount of data limited. Lag times become an issue because of the daisy-chain effect. Real-time data messaging cannot be achieved.
As a payload moves down a conveyor, secondary processing of the payload may occur. For example a payload may be wrapped, stacked, sealed, etc. Auxiliary inputs and outputs on the zone controller are used to interface to the device for this processing. This is outside of the normal zone control and the signaling between zone controllers. Special functions are often provided in the zone controller to handle the interface. Often customized functions must be developed.
Some of the existing zone controllers provide auxiliary inputs and outputs. An input triggers the execution of a specific function in the zone controller. The output is also controlled by a function executing on the zone controller. A limited set of functions are available, and are selected through switch settings or connector wiring on the zone controller. The inputs and outputs only affect the zone controller they are connected to, and cannot be used by other zone controllers in the system. Additional wiring is required if used by more than one zone controller.
One example allows for a central point to connect a maximum of eight inputs or outputs to a conveyor. An input can only be assigned to one zone controller. Each output can only be assigned to a single output of one zone controller. As above, an input triggers a specialized function to execute in the zone controller. Likewise, an output is controlled by a function executing in the zone controller. This example requires that a separate enclosure with electronics and connection points be mounted somewhere on the conveyor. This often becomes a logistics problem when it is necessary to interface to multiple devices along the conveyor.
Zone controllers typically offer a set of options or parameters to the user so that the conveyor action can be ‘tuned’ for the particular type of payload it is moving. Some examples are timers, modes, speeds, etc. Many zone controllers on the market use switches and wire jumpers to set these options. More recent zone controllers set these parameters in the controller memory using remote programming tools. Saving the parameters in memory allows for a wider range of options and much more complexity with them. The parameters are stored in non-volatile memory that retains its value when power is removed. The conveyor is put into use and may work flawlessly for a long time. But, issues may arise when a zone controller fails and must be replaced.
When the options are set using switches or wire jumpers, the replacement zone controller is setup like the one it replaced and installed. When the options are in memory and the zone controller fails, it becomes harder. In may have been months or years since the zone controller was first configured and trying to find what the options were can be problematic. It can be difficult to determine if the options were documented for each zone controller in the system. Even if the options where properly documented, the documentation may be difficult to locate—particularly after a long period of time. Experience has revealed that this problem is very common.
After replacing a failed zone controller, some systems requires that the options be manually setup with the configuration tool. Other systems can load an archived file of the configuration (assuming one was saved) from a PC and use it to configure the replacement zone controller. But these methods are time consuming and problematic, and keep the conveyor offline for an extended period.
It should also be noted that no known ZPA controller systems have the ability to be reprogrammed or updated with new features or customize programs. Instead, they must be removed and replaced with newer models. Further, no known ZPA controller systems have the ability to connect with an external network for monitoring or updating.